How does the "yellow fog" get into the back of a car's headlight?
For example right headlight of this car is "foggy" while the left one is clear:
http://slo.craigslist.org/cto/1476803277.html
How does this happen to a car and what can I do to avoid it? I know that there is a way to avoid it considering that my dad has a 10 year old car that hasn't had that but my cousin bought her car 5 years ago and her left headlight is YELLOW.
How can I avoid this on my car?
Thank you and God Bless!
And I've asked my dad how he did and he doesn't know (considering he is not a car person. He just drives them. Lol.)
Since the 1980s, most headlights are made of polycarbonate which has a lot of the same properties as plastic but stronger (think bullet-proof glass). When cars leave the factory the headlights are coated with a UV cured hard coat. This coating from the factory wears off and the sun’s UV rays (and road debris) cause the lens to develop micro-cracks and pitting. This traps the light inside and makes the outside look cloudy. After extended periods of exposure the unprotected lens can become scorched causing it to yellow. 99% of headlight damage is on the outside of the lens. Often it looks like the damage/fogging/yellowing is on the inside but it isn't. All coatings wear out over time - some of them faster than others (that's why your Dad & Cousin have different experiences). Waxing the headlights with a good wax can help prolong their life as well.
There are many buffing compounds and polishes on the market that will temporarily restore most of the clarity to you headlights. However almost every product will need to be re-done every 4-6 months when polishing which adds up for total cost.
Your best option for headlight restoration is a UV-cured hard coat - just like from the factory when new. However there aren't many DIY kits available and the process takes some skill to get it correct. And most people are afraid of it as it involves sanding with progressively finer grits of sandpaper before reapplication of the coating. (The purpose of sanding is to remove the old coating, the fine layer of oxidization, and to smooth-out the pits and small imperfections). The best coatings will have a hardener and a high UV protection (much more than a can of clear spray paint will have).
Be wary of anyone selling "snake oils" that will clear up the headlights - they are temporary. And any coating that is applied with a sponge/rag will not give you the uniformity that you need for headlights. You need the coating to have the same index of refraction as the polycarbonate that it is protecting which usually involves a "flow-out" process. This way the light goes where it is supposed to.
BTW - I've been restoring headlights for years now as a professional and have tried all the products available - I KNOW what works and what doesn't. Unfortunately the product I use isn't available to the general public. However, if your craigs ad is correct I do believe there are some servicers in Southern CA that use the same product that I do. You can contact me if you want more info.
If you check the sources below you will find some decent DIY coatings.
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